You could write a custom walker for your wp_nav_menu() call. Short of that, I don't think there's anyway to do what you're trying to do.

You could pass such arguments to your fallback function (e.g. wp_list_pages() or wp_page_menu()), but the list-item order of wp_nav_menu() is entirely dependent upon the user-defined menu applied to the given menu location.

Thanks Chip! It's not often you "can't" do something in WordPress. Funny you answered this question, I just emailed you through your website about a plugin question! What a coincidence!
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Drew BakerApr 18 '11 at 18:40